206 C/n-i-sfmas l^/aiid. 



THE FOSSIL CORALS OF CHRISTMAS ISLa:^D. 

 By Dr. J. W. Geegory, F.G.S., F.Z.S. 



(PLATE XIX.) 



The collection of fossil Corals made in Christmas Island by 

 Mr. C. W. Andi'ews includes a little over seventy specimens, 

 which were carefully collected, the exact stratigraphical position 

 of each being recorded. The fauna is of interest, as I understand 

 fi'om Mr. Andrews that no fossils were obtained by previous 

 visitors to Christmas Island, and that the only other fossils which 

 he obtained were foraminifera and a few imperfect molluscan shells. 

 Hence the detennination of the geological age of the various lime- 

 stones that build up the island must be dependent to a considerable 

 extent on the evidence of the corals. 



Many of the specimens, however, have been so altered, often 

 by phosphatization, that they are specifically indeterminable ; and 

 the number of corals collected from the oldest limestones in 

 Christmas Island is small, and the specimens fragmentaiy. But 

 the most serious difficulty in the study of this fauna is that it 

 comes from the borderland between the provinces of the 

 neontologist and palteontologist. The identification of late 

 Cainozoic fossil corals is always a difficult task. For the 

 description of the recent specimens is based on the external fonn 

 and superficial characters ; whereas the description of the fossil 

 corals refers to the essential structure of the corallites, as shown 

 by transverse sections. Hence, consideration of the relations of 

 the living and the latest extinct species of corals involves a 

 comparison of incomparable terms. 



A further difficulty in the case of the Christmas Island 

 collections is introduced by the fact that the corals are mainly 

 Astreans. And the Astreans in the Zoological Department are 

 not j'et arranged, so that I have not always been able to compare 

 the fossil corals with specimens of the species to which they are 

 referred. 



The fauna includes representatives of nineteen determinable 

 species, of which eight are new. 



As regards the general character of the fauna, it is typically 

 Indo-Pacific, all the previously known species coming fi'om that 

 region. 



The corals are all reef-building species, and probably none of 

 them grew at a greater depth than six or eight fathoms. The 

 list of species and their distribution are given in the appended 

 table. The horizons of the fossils have been divided into four 



